The developing fetus normally receives the majority of its nutrients through the fetal placental circulation. Nutrients are also absorbed by the fetal gastrointestinal tract from swallowed amniotic fluid. When placental function is inadequate to meet the needs of the growing fetus, nutritional supplementation through the disgestive tract may be possible. Using a chronic sheep preparation, with indwelling fetal and maternal catheters, we will evaluate the quantitative contribution of gastrointestinal adsorption to fetal nutrition and to what extent this can safely be increased in the normal and compromised fetus. Gastrointestinal and umbilical uptake of glucose, fructose, amino acids, lactate, acetate and oxygen will be determined from measurements of the concentration of these substances in fetal blood entering and leaving the gastrointestinal tract and placenta and from measurements of blood flow to these organs. The relative importance of these two routes in supplying the fetus with nutrients will be compared. The extent to which gastrointestinal uptake can be increased will be evaluated by infusing nutrients into the fetal esophagus. Fetal oxygen consumption, acid-base balance, blood urea nitrogen and ammonia concentrations will be measured when gastrointestinal absorption is increased. The response of the normal fetus will be compared to that of fetuses made hypoxemic by having their mother breathe 10% oxygen and to that of fetuses experimentally growth retarded. Before intrauterine feeding is attempted clinically, we must be certain that hypoxemic and growth retarded animals can absorb nutrients through their gastrointestinal tracts and can increase this absorption without becoming compromised.